Molecules form crystals because of the existence of intermolecular forces. The intermolecular potential energy may be expressed as a sum of non-bonded interatomic terms of the semiempirical Buckingham (exp-6-1) form: Vij equals bibj exp(-(ci plus j)rij)-aiajrij-6 plus qiqjrij-1. This function is applied to atoms i and j (in different molecules) separated by distance rij. Except for monatomic molecules, the present state of theory does not allow accurate calculation of the coefficients. The hardness parameters ck may be estimated from known atomic and moelcular wave functions. Empirical values for ak, bk and qk may be obtained from known crystal structures. The nonbonded parameters thus derived may be used to understand the energetics and geometry of molecular packing. The semiempirical intermolecular potential may also be used to predict the crystal packing structure in cases where the crystal structure has not been experimentally determined. Theoretical estimates may be obtained for such physical quantities as the unit cell dimensions of the crystal, the translational position of the molecule in the unit cell, and the rotational orientation of the molecule in the unit cell. The heat of sublimation and the anisotropic elastic constants of the crystal may also be calculated. By applying a clamping force to the model the effects of high pressure on the crystal may be theoretically studied, including the study of pressure-induced phase transitions.